In the conventional tackles of the type defined hereinbefore, the flexible line is formed usually by a chain and the rotary driving means by a sheave or pulley whose groove is apertured in the shape of the links of the chain and around which the chain is wound only in a fraction of a turn. Beyond this sheave (at the end opposed to the hoisting hook), the chain hangs more or less freely and encumbers the space located below the tackle or is received in a large container which creates difficulties of placement and balancing of the tackle. In other tackles, the chain is replaced by a round cable but this arrangement results also in drawbacks well-known in the art such as the overall size of the drum-pulley usually in width (see U.S. Pat. No. 4,042,213), fragility, necessity to employ a cable guide, etc.
In tackles without pulley-block means, it has often been proposed to employ a flat flexible line (textile strap, steel band, metal braid). In this respect, there may be cited the German patent or patent application Nos. 682,482, 1,120,093, 1,152,237, 2,312,604, 2,700,948, the French patent 996,125 and the U.S. Pat. No. 3,452,964. In these known tackles, the flat flexible line is wound around the drum-pulley to a small height since it is possible to maintain the thickness of this flexible line, i.e. the thickness of each coil on the drum-pulley, to relatively low values because advantage can be taken of the width of this flexible line for increasing its tensile strength.
It is known that loads suspended from a tackle usually undergo a certain amount of lateral swinging. Up to the present time, this phenomenon has prevented replacing the cables or chains, in tackles having pulley-block means comprising an upper block and a lower block, by flat flexible lines, since said lateral swinging would subject these flat flexible lines to lateral forces which would tend to cause them to come out of the various pulleys guiding them.